d6c81f8594
With
set_option showInferredTerminationBy true
this prints a message like
Inferred termination argument:
termination_by
ackermann n m => (sizeOf n, sizeOf m)
it tries hard to use names that
* match the names that the user used, if present
* have no daggers (so that it can be copied)
* do not shadow each other
* do not shadow anything from the environment (just to be nice)
it does so by appending sufficient `'` to the name.
Some of the emitted `sizeOf` calls are unnecessary, but they are needed
sometimes with dependent parameters. A follow-up PR will not emit them
for non-dependent arguments, so that in most cases the output is pretty.
Somewhen down the road we also want a code action, maybe triggered by
`termination_by?`. This should come after #2921, as that simplifies that
feature (no need to merge termination arguments from different cliques
for example.)
25 lines
577 B
Text
25 lines
577 B
Text
/-!
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Another “tricky” example from “Finding Lexicographic Orders for Termination Proofs in
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Isabelle/HOL” by Lukas Bulwahn, Alexander Krauss, and Tobias Nipkow,
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10.1007/978-3-540-74591-4_5.
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Works out of the box!
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-/
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set_option showInferredTerminationBy true
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mutual
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def pedal : Nat → Nat → Nat → Nat
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| 0, _m, c => c
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| _n, 0, c => c
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| n+1, m+1, c =>
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if n < m
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then coast n m (c + m + 1)
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else pedal n (m + 1) (c + m + 1)
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def coast : Nat → Nat → Nat → Nat
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| n, m , c =>
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if n < m
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then coast n (m - 1) (c + n)
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else pedal n m (c + n)
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end
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